1. Field of the Invention
The present invention relates to an electric discharge tube for high-speed axial-flow discharge pumping type gas lasers utilizing a high-frequency electric discharge, and more particularly, to an electric discharge gas laser tube providing a laser light in a rectangular beam mode.
2. Description of the Related Art
Recent developments in high-power lasers and peripheral processing technologies have enabled a wider use of laser beams for welding metals and nonmetals and for surface treatment processes in industry. However, a circular beam mode cannot be used to obtain a uniform processing accuracy, and thus a rectangular beam mode is required for such applications.
FIG. 4 is a schematic illustration of a conventional electric discharge tube for a gas laser. In the Figure, 21 designates a discharge tube, 22a and 22b denote metal electrodes, and 23 designates a high-frequency power source which supplies a high-frequency power of 2 MHz to a fast-flowing laser gas 24 in a discharge tube 21, via the metal electrodes 22a and 22b.
The sectional form of a laser beam output from the gas laser discharge tube is circular, as designated by 24 in FIG. 5(a), and thus the transverse mode is approximately represented by a Gaussian mode as shown by 25 in FIG. 5(b).
Therefore, to carry out a welding and surface treatment processing (e.g., surface hardening), an operation is required to convert the circular beam mode to a rectangular beam mode, and usually this is effected by the use of a paraboloid converging mirror, called a segmented mirror, disposed at the end of a processing head. An example of this is disclosed in a Japanese Unexamined Patent Publication No. 63-77178.
The segmented mirror, however, is arranged such that a large number of small plane mirrors are disposed on a parabolic surface, and thus is very expensive due to its intricate shape.